Chalcone derivatives as fluorescence turn-on chemosensors for cyanide anions

Article abstract of DOI:10.1016/j.jphotochem.2012.06.012

Three o-hydroxy chalcone derivatives 1-3 with carbazolyl (1), pyrene (2) and 4-nitrobenzene (3) as terminal group have been synthesized. Their crystal structures, photophysical properties in CH₃CN and recognition properties for cyanide anions h

Full text of DOI:10.1016/j.jphotochem.2012.06.012

Journal of Photochemistry and Photobiology A: Chemistry 244 (2012) 65–70
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Chalcone derivatives as fluorescence turn-on chemosensors for cyanide anions
Yunhui Suna, Huihui Chena, Duxia Caoa,b,∗, Zhiqiang Liub,∗∗, Hongyu Chenc, Yunlong Denga, Qi Fangb
a School of Material Science and Engineering, Shandong Provincial Key Laboratory of Preparation and Measurement of Building Materials, University of Jinan, Jinan 250022, Shandong,
China
b State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong, China
c Faculty of Chemistry and Chemical Engineering, Taishan Medical University, Taian 271016, Shandong, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three o-hydroxy chalcone derivatives 1–3 with carbazolyl (1), pyrene (2) and 4-nitrobenzene (3) as ter-
minal group have been synthesized. Their crystal structures, photophysical properties in CH3CN and
recognition properties for cyanide anions have also been examined. The research indicates that the
stronger electroaffinity of the chalcone derivative’s ␤-unit is beneficial to Michael reaction and can
improve the response rate of the compound to cyanide anions. These compounds are found to be able to
recognize cyanide anions with fluorescence turn-on response. Especially, compound 3 with strong elec-
tron accepting group exhibits remarkable response to cyanide anions in CH3CN H2O (1:1, v/v) solution
with a ca. 40-fold intensity enhancement.
Received 19 March 2012
Received in revised form 24 May 2012
Accepted 18 June 2012
Available online 26 June 2012
Keywords:
Chalcone derivative
Cyanide anion
© 2012 Elsevier B.V. All rights reserved.
Chemosensor
Turn-on fluorescence
Michael acceptor
Crystal structure
1. Introduction
nucleophilicity of cyanides to the carbon cation [5,14–27]. Recently,
Kim group discovered a chalcone derivative (2ꢀ-hydroxyl-4ꢀꢀ-
It is well known that cyanide anions (CN−) are extremely toxic
to living organisms, and trace scale intake of cyanides may result
in the death. However, cyanides are still widely used as irreplace-
able industrial materials in some fields including synthetic resin,
medicine, pesticide, fertilizer, gold and silver extraction [1–3].
World Health Organization sets the maximum permissive level of
cyanide in drinking water is at 1.9 ␮M [4,5]. So, cyanide detection is
very important to environmental concern, food analysis and even
anti-terrorism [6,7].
dimethylamino-chalcone (0)), which showed a highly fluorescence
turn-on response for the cyanide anion [28]. The o-hydroxy group is
believed to play an important role in activating this chalcone com-
pound as Michael acceptor to react with cyanide anion.
Over the past ten years, optical chemosensors for cyanide anion,
in which a change in color, fluorescence intensity or spectral posi-
tion corresponding to the chemical interaction between sensor
and cyanide is monitored, have attracted growing interests due
to their simple, inexpensive, and rapid implementation [3,8–13].
Generally, optical chemosensors for cyanides are designed based
on the characteristic properties of cyanide anion, such as its
strong nucleophilicity, high binding affinity and similarity with
halogen anion (CN− is also called pseudohalogen). For example,
most of chemodosimeter approaches are based on the exceptional
Our group is devoted to the research on chalcone derivatives
for several years [29,30]. During the course of our ongoing efforts
toward developing novel chemosensor for cyanides [31,32], chal-
cone derivatives were also examined. In this paper, three chalcone
derivatives 1–3 with carbazolyl (1), pyrene (2) and 4-nitrobenzene
(3) as terminal group, have been synthesized and their crystal struc-
tures and recognition properties for cyanide anions have also been
examined. Varied electron donating or accepting group were intro-
duced to tune the intramolecular hydrogen bond and then affect
responsibility to cyanide anions.
2. Experimental
∗
Corresponding author at: School of Material Science and Engineering, Shandong
Provincial Key Laboratory of Preparation and Measurement of Building Materials,
University of Jinan, Jinan 250022, Shandong, China. Tel.: +86 531 8973 6751;
fax: +86 531 8797 4453.
2.1. Synthesis and characterization
∗∗
The synthetic routes of chalcone derivatives 1–3 and corre-
sponding cyanide bonding compounds 1-CN and 2-CN are shown
Corresponding author Tel.: +86 531 8836 2782; fax: +86 531 8836 2782.
E-mail addresses: duxiacao@ujn.edu.cn (D. Cao), zqliu@sdu.edu.cn (Z. Liu).
1010-6030/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jphotochem.2012.06.012

66
Y. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 244 (2012) 65–70
Scheme 1. Synthetic routes of compounds 1–3.
in Scheme 1. 2-(Hydroxy)acetophenone, pyrrolidine, pyrene-1-
carboxaldehyde and p-nitrobenzaldehyde were purchased from
Aladdin Reagents. N-ethyl-carbazole-3-aldehyde, tetrabutylam-
monium cyanide and other chemicals were used as received from
Shanghai Reagents. NMR spectra were recorded on a Bruker Avance
III 400 MHz spectrometer at ambient temperature. Mass spectra
were recorded on an Agilent Q-TOF6510 spectrometer. Elemental
analyses were carried out on a PE 2400 autoanalyzer.
Calcd exact mass: 369.1603, found 369.1616. Anal. Calcd for
24H20N2O2: C, 78.24; H, 5.47; N, 7.60; Found C, 78.18; H, 5.52; N,
7.64.
Synthesis of 2. Compound
to compound using pyrene-1-carboxaldehyde and 2-
C
2
was synthesized similar
1
(hydroxy)acetophenone as the starting materials. Orange solid
(0.25 g, yield 68%). 1H NMR (CDCl3, 400 MHz), ı (ppm): 7.00 (t,
J = 7.6 Hz, 1H), 7.08 (d, J = 8.4 Hz, 1H), 7.55 (t, J = 7.8 Hz, 1H), 7.96
(d, J = 15.2 Hz, 1H), 8.04–8.08 (m, 2H), 8.07 (d, J = 7.6 Hz, 1H), 8.10
(d, J = 8.8 Hz, 1H), 8.17 (d, J = 8.8 Hz, 1H), 8.22 (d, J = 8.8 Hz, 1H),
8.25–8.28 (m, 2H), 8.46 (d, J = 8.0 Hz, 1H), 8.61 (d, J = 9.2 Hz, 1H),
9.13 (d, J = 15.2 Hz, 1H), 12.99 (s, 1H). 13C NMR (CDCl3, 100 MHz),
ı (ppm): 118.74, 118.92, 120.24, 122.05, 122.53, 124.35, 124.63,
125.07, 125.10, 126.13, 126.28, 126.44, 127.35, 128.44, 128.99,
129.03, 129.73, 130.64, 130.76, 131.35, 133.30, 136.41, 142.12,
163.78, 193.51. MS for (M+H)+, Calcd exact mass: 349.1229, found
349.1231. Anal. Calcd for C25H16O2: C, 86.19; H, 4.63; Found C,
86.08; H, 4.68.
Synthesis of 2-CN. Compound 2-CN was synthesized similar
to 1-CN. Pale-yellow solid (0.17 g, yield 86%) 1H NMR (CDCl3,
400 MHz), ı (ppm): 3.72 (dd, J = 4.0 Hz, J = 18 Hz, 1H), 4.05 (dd,
J = 9.6 Hz, J = 18 Hz, 1H), 5.60 (dd, J = 4.4 Hz, J = 9.6 Hz, 1H), 6.85 (t,
J = 7.6 Hz, 1H), 7.03 (d, J = 8.4 Hz, 1H), 7.49 (t, J = 7.8 Hz, 1H), 7.61 (d,
J = 8.0 Hz, 1H), 8.07 (t, J = 7.6 Hz, 1H), 8.09 (d, J = 8.8 Hz, 1H), 8.14 (d,
J = 8.8 Hz, 1H), 8.18 (d, J = 9.6 Hz, 1H), 8.23 (d, J = 9.6 Hz, 1H), 8.25 (d,
J = 7.6 Hz, 3H), 8.30 (d, J = 8.4 Hz, 1H), 11.94 (s, 1H). 13C NMR (CDCl3,
100 MHz), ı (ppm): 29.13, 43.91, 118.67, 118.92, 119.28, 120.68,
120.98, 124.69, 125.28, 125.31, 125.53, 125.82, 126.13, 126.51,
127.30, 127.52, 128.23, 129.27, 129.39, 130.51, 131.33, 131.67,
137.25, 162.68, 200.40. MS for (M+H)+, Calcd exact mass: 376.1338,
found 376.1298. Anal. Calcd for C26H17NO2: C, 83.18; H, 4.56; N,
3.73; Found C, 83.06; H, 4.58; N, 3.76.
Synthesis of 3. Compound 3 [33] was synthesized similar to
1 with p-nitrobenzaldehyde and 2-(hydroxy)acetophenone as the
starting materials. Yellow solid (0.62 g, 46% yield): 1H NMR (CDCl3,
400 MHz), ı (ppm): 6.98 (t, J = 7.6 Hz, 1H), 7.06 (d, J = 8.4 Hz, 1H),
7.54 (t, J =7.8 Hz, 1H), 7.76 (d, J = 15.6 Hz, 1H), 7.81 (d, J = 8.8 Hz, 2H),
7.91 (d, J = 9.0 Hz, 1H), 7.93 (d, J = 15.4 Hz, 1H), 8.30 (d, J = 8.8 Hz,
2H), 12.56 (s, 1H). 13C NMR (CDCl3, 100 MHz), ı (ppm): 118.88,
119.11, 119.80, 124.18, 124.30, 129.14, 129.68, 137.03, 140.72,
142.11, 148.80, 163.78, 193.01. MS for (M+H)+, Calcd exact mass:
270.0766, found 270.0735. Anal. Calcd for C15H11NO4: C, 66.91; H,
4.12; N, 5.20; Found C, 66.98; H, 4.10; N, 5.17.
Synthesis
of
1
[29].
0.6 mL
(5.0 mmol)
2-(hydroxy)acetophenone, 1.12 g (5.0 mmol) N-ethyl-carbazole-
3-aldehyde and 0.4 mL (5.0 mmol) pyrrolidine were dissolved
in 15 mL ethanol. The mixture was stirred overnight at room
temperature to afford compound 1 as yellow precipitates. The
solid was filtered, washed twice with ethanol and dried in vacuum
(1.31 g, yield 77%). 1H NMR (CDCl3, 400 MHz), ı (ppm): 1.47 (t,
J = 7.2 Hz, 3H), 4.39 (q, J = 7.2 Hz, 2H), 6.97 (t, J = 7.6 Hz, 1H), 7.04 (d,
J = 8.4 Hz, 1H), 7.30 (t, J = 7.4 Hz, 1H), 7.42 (d, J = 4.0 Hz, 1H), 7.45 (d,
J = 4.0 Hz, 1H), 7.49 (d, J = 7.2 Hz, 1H), 7.53 (d, J = 8.4 Hz, 1H), 7.71 (d,
J = 15.2 Hz, 1H), 7.81 (d, J = 8.4 Hz, 1H), 8.02 (d, J = 8.0 Hz, 1H), 8.16
(d, J = 7.6 Hz, 1H), 8.17 (d, J = 15.2 Hz, 1H), 8.40 (s, 1H), 13.11 (s, 1H).
13C NMR (CDCl3, 100 MHz), ı (ppm): 13.85, 37.84, 108.99, 116.78,
118.58, 118.70, 119.88, 120.33, 120.69, 121.98, 122.87, 123.61,
125.71, 126.48, 126.66, 129.56, 135.95, 140.55, 141.75, 147.20,
163.61, 193.65. MS for (M+H)+, Calcd exact mass: 342.1494, found
342.1486. Anal. Calcd for C23H19NO2: C, 80.92; H, 5.61; N, 4.10;
Found C, 80.66; H, 5.63; N, 4.12.
Synthesis of 1-CN. 0.34 g (1.0 mmol) of 1 and 10 equiv. tetra-
butylammonium cyanide (TBACN) were dissolved in 50 mL CH3CN
in a flask. The mixture was stirred overnight at room temperature
and then the solvent was removed under reduced pressure and
the residue was extracted with dichloromethane (50 mL× 3) from
acidic aqueous solvent and separated by column chromatography
using dichloromethane as the eluent to afford the desired 1-CN as
a light yellow solid (0.34 g, yield 92%). 1H NMR (CDCl3, 400 MHz),
ı (ppm): 1.43 (t, J = 7.2 Hz, 3H), 3.64 (dd, J = 5.6 Hz, J = 18 Hz, 1H),
3.86 (dd, J = 8.4 Hz, J = 18 Hz, 1H), 4.37 (q, J = 7.2 Hz, 2H), 4.71 (dd,
J = 6.0 Hz, J = 5.6 Hz, 1H), 6.88 (t, J = 7.8 Hz, 1H), 7.00 (d, J = 8.4 Hz, 1H),
7.26 (t, J = 7.6 Hz, 1H), 7.42 (dd, J = 8.4 Hz, J = 3.2 Hz, 2H), 7.46–7.52
(m, 3H), 7.65 (d, J = 8.0 Hz, 1H), 8.11 (d, J = 7.6 Hz, 1H), 8.15 (s,
1H), 11.92 (s, 1H). 13C NMR (CDCl3, 100 MHz), ı (ppm): 13.79,
31.82, 37.70, 44.83, 108.74, 109.21, 118.78, 118.82, 119.22, 119.30,
119.48, 120.62, 121.08, 122.37, 123.53, 124.76, 125.03, 126.33,
129.42, 137.06, 139.65, 140.47, 162.57, 200.58. MS for (M+H)+,

Y. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 244 (2012) 65–70
67
Table 1
Crystal data, data collections, and structure refinements of compounds 2 and 3.
Crystal data
2
3
Empirical formula
Formula mass
Crystal system
Space group
C25H16O2
348.38
C15H11NO4
269.25
Monoclinic
P21/c
7.431(2)
12.954(4)
13.270(4)
94.463(4)
1273.5(7)
4
Orthorhombic
P21 21 21
4.964(5)
13.019(5)
26.727(5)
90.00
1727.3(19)
4
1.34
˚
a [A]
˚
b [A]
˚
c [A]
ˇ [◦]
3
˚
V [A ]
Z
ꢀcalc [g cm−3
]
1.404
0.103
560
ꢁ [mm−1
F(0 0 0)
]
0.084
728
Crystal size [mm]
ꢂmin − ꢂmax [◦]
T [K]
0.15 × 0.12 × 0.10
3.05–26.00
293(2)
0.24 × 0.09 × 0.07
2.20–27.48
296(2)
Scan mode
Index range
␻, ␸
␻, ␸
−6 ≤ h ≤ 6
−16 ≤ k ≤ 14
−32 ≤ l ≤ 32
5987
3135
246
−9 ≤ h ≤ 9
−13 ≤ k ≤ 16
−16 ≤ l ≤ 17
7676
2895
183
Collected reflections
Unique reflections
Refined parameters
R1, wR2
0.0909, 0.2813
0.286, −0.270
0.0666, 0.1960
0.170, −0.202
Fig. 1. The molecular structures of compound 2 (a) and compound 3 (b).
−3
˚
ꢀfin (max., min.) [e A
]
Several efforts to get pure compound 3-CN were failed because
of the poor stability.
compounds are trans-conformation and this was also proved by
the single crystal diffraction results. No cis-isomers were detected
[35]. To investigate the reactive site of Michael addition, corre-
sponding cyanide bonding compounds were also prepared and
purified. Compared with that of compound 1, the 1H NMR spec-
trum of compound 1-CN is obviously different resulting from the
Michael addition of the cyanide anions to the enone of 1. For exam-
ple, the signal of vinylic protons in 1 (8.17 and 7.71 ppm, with
J = 15.2 Hz) disappeared and three groups of new peaks appear at
3.64, 3.86, and 4.71 ppm, which should be corresponding to the
protons bonding to C8 and C9. The fine structures in 1H NMR of
1-CN also seem indicating the chiral carbon center of C9 after the
Michael addition. Furtherly, 13C NMR of 1-CN also clearly shows
the difference. Two aliphatic peaks at 44.83 and 31.82 ppm indicate
the product of the Michael addition. Similar to that of compound
1-CN, the NMR spectra of compound 2-CN also clearly show three
groups of new peaks at 5.60, 4.05 and 3.72 ppm in 1H NMR and
two aliphatic peaks at 43.91 and 29.13 ppm in 13C NMR. Furtherly,
the mass spectra and elemental analyses also support the assumed
Michael addition product. What should be pointed out, although
1-CN and 2-CN can be obtained successfully, the nitro-substituted
compound is failed. This compound seems quite unstable during
the column chromatography process and acidic workshop.
The crystal structures of compounds 0 and 1 had been published
by us previously [29,30], and the single crystal structures of 2 and 3
(Fig. 1 and Table 1) were also obtained recently. Unfortunately, all
the efforts to grow the single crystal of 1-CN and 2-CN are failed. The
dihedral angles between benzoyl groups and the phenyl rings of the
aniline (0 and 1), pyrene ring (2) or nitrobenzene ring (3) are shown
in Table 2. Although the dihedral angles between benzoyl group and
the phenyl ring vary with different terminal groups, these com-
pounds are generally planar. For compound 1, the dihedral angle is
similar to that of compound 0. But the dihedral angle of compound 2
is obviously bigger than that of 0 and 1. The planarity of compound
3 is the best with the dihedral angle being only 3.08◦. There are also
some noticeable conjugation in the C10 C9 C8 C7 bridge of com-
pounds 0–3 between the benzoyl groups and the phenyl rings, as
indicated by the stretched C8 = C9 double bond and shrank C7 C8
and C9 C10 single bonds.
2.2. Photophysical properties and response to cyanide anions
Solutions of compounds 1–3 with 10 ␮M in CH3CN or
CH3CN H2O (1:1, v/v) were prepared for photophysical measure-
ments. UV–vis absorption and steady-state fluorescence spectra
were recorded at room temperature on a Shimadzu UV2550
spectrophotometer and an Edinburgh FLS 920 spectrometer,
respectively. The compounds were titrated with cyanide anions by
the addition of a solution TBACN in CH3CN. The spectral changes
were monitored with the varied equivalent of CN− and reaction
time. The fluorescence quantum yields ˚ were measured by using
a standard method with quinine sulfate as the standard [34].
2.3. Structure determination
Single crystal of compound 2 was obtained by slow diffu-
sion of n-hexane into a solution of the compound in chloroform
(CHCl3). X-ray diffraction data of an orange single crystal of 2
(0.15 mm × 0.12 mm × 0.10 mm) was collected on a Gemini CCD
X-ray single crystal diffractometer. Single crystal of compound 3
was obtained by slow evaporation of a solution of the compound in
CHCl3. X-ray diffraction data of a yellow single crystal of compound
3 (0.24 mm × 0.08 mm × 0.04 mm) was collected on a Bruker Smart
APEX-II CCD X-ray single crystal diffractometer. Crystal data, data
collections and structure refinements of compounds 2 and 3 are
shown in Table 1.
3. Results and discussion
3.1. Synthesis and molecular structures
All these chalcone derivatives 1–3 were synthesized by ordi-
nary condensation reaction of the 2-(hydroxy)acetophenone with
different aryl-aldehydes in good yields as the routes in Scheme 1.
These compounds were fully characterized by NMR, mass spectra
and elemental analyses. The coupling constant of vinylic protons of
compounds 1–3 is nearly 15 Hz, which clearly indicates that these

68
Y. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 244 (2012) 65–70
Table 2
◦
˚
Selected geometric parameters (A, ) of the crystal structures.
Dihedral angle ˛, (◦)a
˚
˚
˚
˚
˚
˚
˚
C1 O1 (A)
C1 C6 (A)
C6 C7 (A)
C7 O2 (A)
C7 C8 (A)
C8 C9 (A)
C9 C10 (A)
0
1
2
3
1.352(4)
1.347(3)
1.343(10)
1.345(4)
1.410(4)
1.397(3)
1.389(13)
1.403(4)
1.472(4)
1.471(3)
1.441(12)
1.457(4)
1.254(4)
1.250(3)
1.268(9)
1.239(3)
1.447 (4)
1.457(3)
1.459(12)
1.468(4)
1.344 (4)
1.328(3)
1.335(10)
1.320(4)
1.431 (4)
1.454(3)
1.425(11)
1.463(4)
10.28
11.12
24.62
3.08
a
The dihedral angles of benzoyl group and the phenyl ring (C10 C15).
3.2. Spectral response to cyanide anion complexation
under the pseudo first-order reaction conditions [25]. These data
clearly indicate that compound 3 exhibit stronger bonding interac-
tion with cyanide anions than other compounds. So, it seems that
the stronger electroaffinity of the chalcone-derivative’s ␤-unit is
beneficial to Michael reaction and can improve the response rate
of the compound to cyanide anions.
Linear absorption spectra of compounds 1–3 in CH3CN are
shown in Fig. 2. Compounds 0–3 are chalcone derivatives with
similar molecular structures and different electron donor or accep-
tor groups. The accepting electron ability of terminal group is in a
sequence
nitrobenzene > pyrene > carbazolyl > dimethylamino.
1 exhibits strong linear absorption at 405 nm
What should be more interesting, further investigation indicates
that compound 3 can response to cyanide anions in aqueous sys-
tem. As shown in Fig. 4, upon the addition of cyanide anion, a new
absorption band appeared at 256 nm and increased by time, with
the simultaneous gradual disappearance of the band at 322 nm.
The complexation is saturated after 2 h with an isoabsorptive point
at 277 nm. The influence of other anions such as F−, Cl−, Br−, I−,
HSO4−, NO3−, H2PO4−, AcO−, and SCN− have also been examined.
These anions induced negligible absorption changes, therefore the
compounds exhibit excellent selectivity to cyanide anions.
The pH range within which compound 3 remains stable was
investigated. The absorbance of compound 3 at 322 nm was
Compound
with ε = 5.61 × 104 M−1 cm−1
.
Compound
2
exhibits vibrated
and 424 nm
2 possesses weaker
structure at 392 nm (ε = 2.71 × 104 M−1 cm−1
)
(ε = 2.82 × 104 M−1 cm−1). Even though
charge transfer compared to 1 because of the weaker electron
donating ability of pyrene group, its absorption peak exhibits
slight red shift, which may be derived from larger conjugated
structure of pyrene group. Compared to other two compounds,
compound 3 exhibits shorter absorption peak with ꢃmax 319 nm
(ε = 3.42 × 104 M−1 cm−1), which may be derived from the strong
electron accepting ability of nitro group and then it is a A–␲–Aꢀ
type of molecule.
To examine the cyanide-recognizing properties of these com-
pounds, tetrabutylammonium cyanide n-Bu4NCN (TBACN) as a
cyanide source was added to a solution of compounds 0–3 in
CH3CN. Time-dependent UV–vis spectral changes upon addition
of CN− to compounds 1–3 in acetonitrile are shown in Fig. 3. As
shown in Fig. 3(a), upon complexation with CN−, the character-
istic intense charge-transfer absorption band of compound 1 at
405 nm gradually decreases and after 13 h, 1 bonds with cyanide
anions completely. Compound 2 exhibits similar spectra response
(Fig. 3(b)) to cyanide anions with 1, the absorption band at 424 nm
gradually decreases and new bands at 265 nm, 276 nm, 326 nm and
342 nm are attended and gradually increase and after 8.0 h, the
complexation is finished.
Spectral experiments also indicate that different com-
pounds show greatly different response rate to the addition
of cyanide anions. The kinetic analysis gave the rate constants
k(1) = 7.2 × 10−5 s−1, k(2) = 6.7 × 10−4 s−1 and k(3) = 1.8 × 10−3 s−1
Fig. 3. Time-dependent UV–vis spectral changes upon addition of 30 equiv. CN− to
1 (a, 10 ␮M in CH3CN) and 5 equiv. CN− to 2 (b, 20 ␮M in CH3CN). Insert: plot of
absorption intensity at 405 nm (1) and 342 nm, 424 nm (2) versus time.
Fig. 2. Linear absorption spectra of compounds 1–3 in CH3CN with C = 10 ␮M.

Y. Sun et al. / Journal of Photochemistry and Photobiology A: Chemistry 244 (2012) 65–70
69
(3). The weak fluorescence emission and low quantum yields of
the compounds 1–3 are maybe due to the ultrafast intramolecu-
lar hydrogen atom transfer and/or ultrafast deactivation processes
such as intersystem crossing and internal conversion through
the hydrogen bonding [30,33,35]. However, their fluorescence
intensity and quantum yields increase smartly with the addi-
tion of cyanide anion with quantum yields being 0.1 (1 added
cyanide anions), 0.05 (2 added cyanide anions) and 0.041 (3
added cyanide anions). That is to say, the compounds are able
to recognize cyanide anions with fluorescence turn-on response.
After the addition of cyanide anions, compound 1 in CH3CN solu-
tion shows strong blue fluorescence emission with ꢃmax 468 nm
and the fluorescence intensity exhibits 80-fold enhancement with
17 nm red shift. Compound 2 exhibits similar spectral response
with 10-fold intensity enhancement upon the addition of cyanide
anions. Especially, compound 3 can recognize cyanide anions
in CH3CN H2O (1:1, v/v) solution with a ca. 40-fold intensity
enhancement.
Fig. 4. Time-dependent UV–vis spectral changes upon addition of 30 equiv. CN− to
compound 3 (10 ␮M in CH3CN H2O (1:1, v/v)). Insert: plot of absorption intensity
at 322 nm versus time.
4. Conclusion
monitored as a function of pH. As shown in Fig. S11, compound 3
remains stable with pH value changing from 5.0 to 10.0, but when
pH value is larger than 10.3, the absorbance at 322 nm decreases
and exhibit similar spectra change with the addition of cyanide.
After 30 equiv. CN− was added to compound 3 solution in water, the
pH is 9.4, which indicates that compound 3 should be stable with-
out the addition of cyanide in this pH environment. pH-dependence
for the CN− response was also investigated. From Fig. S12, we can
see the compound exhibit similar response to CN− in pH range
6.0–10.0.
In summary, the effectiveness of three chalcone derivatives as
chemosensor for cyanide anions were demonstrated. The chalcone
derivative 3 with nitrobenzene as terminal electron acceptor group
can recognize cyanide anions in CH3CN H2O (1:1, v/v) solution. The
further investigation following this way should be possible to find
more efficient cyanide sensor for ground application.
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (20802026, 50803033), Natural Science Foundation
of Shandong Province (Q2008F02), Shandong Encouraging Fund for
Excellent Scientists (BS2009CL013) and Science and Technology
Star Funds of Jinan (20110314).
The detection limits [28,36,37] for CN− are also provided.
Fluorescence changes by increasing the amount of cyanide was
measured (Fig. S13). The detection limit of compounds 1–3 are
ca. 2.1 ␮M (1 in CH3CN), 0.8 ␮M (2 in CH3CN) and 7.2 ␮M (3 in
CH3CN H2O (1:1, v/v)).
Fluorescence spectral response of the compounds to cyanide
anion complexation was also investigated. Excitation spectra of
compounds 1–3 before and after the addition of TBACN are shown
in Fig. S14. According to excitation spectra, the excitation wave-
lengths are 360 nm (1), 350 nm (2) and 280 nm (3), respectively.
As shown in Fig. 5, compounds 1–3 exhibit weak fluorescence
emission and the quantum yields of the compounds 1–3 are very
low with the values being 0.00075 (1), 0.0035 (2) and 0.0018
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.jphotochem.2012.06.012.
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